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Phosphorus, Plasma / Serum

Item Value
Test Update Information Effective November 4, 2015 , the phosphorous reference range has been modified due to changing from serum to plasma as the preferred sample type. It is known that plasma phosphorous levels run about 0.2 g/dL lower than serum samples which has been verified by in house studies.
Approval req'd? No
Available Stat? Yes
Test code PO4
Test group Phosphorus
Performed by Parnassus, Mission Bay & Mt. Zion Chemistry
In House Availability Test available 24 hours per day 7 days per week
Method Spectrophotometric (molybdate)
Container type Light green top preferred, Gold top acceptable
Amount to Collect 1 mL blood
Click here for Microdetermination info
Sample type Plasma or serum
Preferred volume 0.5 mL plasma or serum
Min. Volume 0.2 mL plasma or serum
Click here for Microdetermination info
Units mg/dL
Normal range
< 1 month 3.7 - 7.7 mg/dL
1 month - 11 months 3.3 - 6.6 mg/dL
1 year - 3 years 2.9 - 6.0 mg/dL
4 years - 12 years 2.8 - 5.7 mg/dL
13 years - 15 years 2.7 - 5.1 mg/dL
≥ 16 years 2.4 - 4.9 mg/dL

1. Normal range for pediatric patients adapted from Soldin, Steven J., "Pediatric Reference Ranges", 6th edition, AACC Press, 2007, method 1.
2. Normal range for adults was determined by testing 271 male and female healthy blood donors at UCSF with the lower limits of normal adjusted to encompass results from plasma specimens.
Critical value < 1.0 mg/dL
Synonyms PO4
Stability Room temperature 8 hours, refrigerated 2 days, frozen at -20C 1 week
Turn around times STAT 1 hour, Routine: 4 hour
Additional information To convert mg/dL to mmol/L (SI units) multiply by 0.323.

Phosphorus, like potassium, is released by platelets during clotting, and serum levels are approx. 0.2 mg/dL higher than those measured in plasma. Levels can be falsely elevated by thrombocytosis, though not as predictably as those for potassium.

High dose liposomal amphotericin B treatment may also cause falsely elevated serum phosphorus values in this DXC assay (see Bailey H and Chan E, Clin Chem 53:795-6, 2007)
CPT coding 84100
LOINC code 2777-1
Last Updated 7/24/2015 8:47:18 AM
Entry Number 740
Lab Procedure Link Click here for Procedure
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